Mojo - Disc brake sizes for Clydesdale...

My LBS talked me into 8" downhill brake rotors on the Mojo. The front pizza-saucer works great. The back, however, is locking up way too easily, especially in those 'uh-oh' situations where I need it most. It's OK when I'm, say, seated and going down a long bomber run; in those cases, I'm able to modulate it fine. When I'm in a slower situation, though, say, slowing down to take a tight turn on roller-coaster terrain, I skid the back almost every time.

OK, now for the actual question... any specific advice between a 7" or 6" rotor on the rear? Which size can I back down to and have the most reasonable expectation of having similar braking behavior to my front rotor?

6' 0" 180lbs here and I have 8" rotors up front and 6" rotors in the rear with Magura Louise FR driving them and I absolutely love the combination.

I laid it on *really* heavy on my front once and nearly endo'd - but didn't. They stop me on a dime when I need them to and give me a great sense of control and confidence in all other occasions. (I have mostly been riding over in Moab since I got the bike.

With your additional ride weight an 8 inch front with 6 in the rear should work great.

BTW, I got some Galfer 185 and 160 rotors, partly for bling and partly for much better mud shedding in the rear than the Hayes which packs mud in the holes. I had to shim the front caliper adapter face out 2.5 mm with simple washers, the rear fit with no fit adjustment. The jingling or rattling of the front rotor at certain speeds on hardpack or pavement from tire vibration I could never adjust out is gone with the slightly more stoutly spoked Galfers. And they are nearly perfectly quiet with the stock Hayes pads with no more occasional honk or squeals.

With your additional ride weight an 8 inch front with 6 in the rear should work great.

BTW, I got some Galfer 185 and 160 rotors, partly for bling and partly for much better mud shedding in the rear than the Hayes which packs mud in the holes. I had to shim the front caliper adapter face out 2.5 mm with simple washers, the rear fit with no fit adjustment. The jingling or rattling of the front rotor at certain speeds on hardpack or pavement from tire vibration I could never adjust out is gone with the slightly more stoutly spoked Galfers. And they are nearly perfectly quiet with the stock Hayes pads with no more occasional honk or squeals.

On long steep technical(loose rutty straights and switchbacks), I tend to overheat my rear brake. I know you are supposed to use your front brake more, but in those situations, where you want to avoid washouts and sliding into ruts, the rear gets a lot of use. Those 6 in. rotors heat up fast, and I wonder about going to the next size up or higher for cooling.
I had replaced my Hayes rear rotor with an Aztec wavy rotor and that didn't help. I replaced my rear wheel with a center lock type and went with an XT rotor. It runs a little cooler(lots of holes), but makes slightly more noise. Is it OK to use larger rotors on the Mojo rear?

On long steep technical(loose rutty straights and switchbacks), I tend to overheat my rear brake. I know you are supposed to use your front brake more, but in those situations, where you want to avoid washouts and sliding into ruts, the rear gets a lot of use. Those 6 in. rotors heat up fast, and I wonder about going to the next size up or higher for cooling.
I had replaced my Hayes rear rotor with an Aztec wavy rotor and that didn't help. I replaced my rear wheel with a center lock type and went with an XT rotor. It runs a little cooler(lots of holes), but makes slightly more noise. Is it OK to use larger rotors on the Mojo rear?

For your lighter weight I'd try the 6 inch in the rear first, with 7 inch in front. If you get brake fade in the rear, then go to 7 inch in the rear too. It will fit. I would think that a 8 inch rotor in front might be overpowered for your weight for good modulation on tight trails.

I went from older 165mm Avid mechanicals still on my Tracer to the Hayes HFX-9 160 mm (6 inch) rotors at first with the Mojo SX build. The Hayes were a little less powerfull. I haven't had a fade problem yet with 7/6 rotors, but haven't yet done the two steepest long DH's I've done before that would fade the Avids.

7"

I just switched from 6" XTR rotors to 7" XTR rotors and am much happier. At 6'4", 175lbs I was overheating the 6" rotors way too easily. I also switched to the resin pads which I find much quieter, smoother, stronger, and more predictable. On my first ride on the 7" rotors (night ride on Wednesday) my rear was locking up a little too easily on the leaves & pine needles. But by my 2nd ride I was used to the added power and now really like it, especially on the steep, rocky descents, and late braking corners.

Thanks!

Originally Posted by davidbelden

I just switched from 6" XTR rotors to 7" XTR rotors and am much happier. At 6'4", 175lbs I was overheating the 6" rotors way too easily. I also switched to the resin pads which I find much quieter, smoother, stronger, and more predictable. On my first ride on the 7" rotors (night ride on Wednesday) my rear was locking up a little too easily on the leaves & pine needles. But by my 2nd ride I was used to the added power and now really like it, especially on the steep, rocky descents, and late braking corners.

I'm 6ft and 207lbs, i run the original saint brakes, 8in rotor up front and 6inch at the rear. I originally found this combination sorely lacking in the power i required, but finally narrowed it down to pads that must've been contaminated.
I swapped the old pads out for a new set of koolstops and have been very happy with them since

I'm seriously considering a switch to Hope Tech M4's but cant decide on the rotor size. Should I go 203F 183R or will that compromise XC riding (except for weight)?

Be sure to replace the brake fluid every year or so, or if you experience increasing fade problems. Brake fluid is designed to absorb and mix with the moisture present in the air which leaches past the seals over time. When the calipers get really hot on longer descents the absorbed water in the brake fluid will expand and act like air in the lines, weakening and fading the brake power.

Also if you are using "organic" type pads try some "sintered" type pads if available for the Hope Minis before spending big bucks on new brakes. The power gain is pretty huge going to the sintered type, and they are claimed to be quieter and more fade resistant.

Perhaps I shouldn't be posting here as I am only about 205 with gear. I ride a large with 2.35 High Roller F and Minion R both super tacky. I have Avid Juicy 7s - 6 inch rotors both ends with sintered pads. I live in a warm climate (Qld Australia) and have ridden many times in temps from 35C up to near 40. I find the rotors work well with one finger and have never experienced fade. I could see a 7 inch front being an advantage on really steep terrain, but as for fade, is this something Avid sintrered pads just do better?

To the OP, I found the 203mm rear disk way to close to the frame, in fact Hans advised that the 203mm was to close to the chain stay back there.
I ended up with 203mm in the front and 180mm in the rear, this is with Juicy 7's. The front are powerful, maybe to much so, I have endoed by panic braking on 2 seperate occasions, both times on me, I have learned to rein myself in and it's working out but, yeah, powerful! The 180mm in the back are just right, they work well. 203mm and 180mm is a perfect combination I think.
YZF571